Ghost cancelling system and control method thereof

ABSTRACT

A ghost cancelling system which detects a horizontal scanning line containing the reference signals and extracts 8 fields reference signals from the horizontal scanning line. A final reference signal corresponding to the 8 fields reference signals is calculated by a specified calculation algorithm, and the system corrects the tap coefficient in response to the distinguished ghost signal using the final reference signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a ghost cancelling system,and more particularly to a ghost cancelling system for cancelling ghostsignals from a video signal using a reference signal of the 8-fieldsequence type.

2. Description of the Related Art

In recent years, use of a ghost cancel reference (hereafter, GCR) signalfor cancelling ghost signals contained in a video signal has becomestandard in television broadcasting systems. For example, this new GCRmethod has been adopted as Japan's standard for broadcasting and wasintroduced in the fall of 1989. The details of GCR signals are given in"Development of a Ghost Cancel Reference Signal for TV Broadcasting",IEEE Trans. on Broadcasting, Vol. 35, No. 4, Dec. 1989, by Miyazawa,Matsuura, Takayama and Usui (hereafter, Ref. 1) which is incorporatedherein by reference. The GCR signal described in this Ref. 1 is known asan 8-field sequence type GCR signal. In this system, the ghost signal iscancelled with the aid of a GCR signal inserted with a period of 8fields in the 18th horizontal scanning line (18H) of the odd numberedfields and the 281st horizontal scanning line (281H) of the evennumbered fields. Further, the ghost signal is detected using the finallycalculated GCR signal (S_(GCR)) that is obtained by performing the8-field sequence calculation indicated by the following equation (1).

    S.sub.GCR =(S.sub.1 -S.sub.5)+(S.sub.6 -S.sub.2)+(S.sub.3 -S.sub.7)+(S.sub.8 -S.sub.4)                              (1)

This operation is performed in order to remove the ghost effect of thehorizontal scanning line signal previous to the horizontal scanning linein which the GCR signal is inserted, and the horizontal synchronizationsignal and color burst signal of the horizontal scanning line in whichthe GCR signal is inserted.

As an example, a conventional ghost cancelling system using a GCR signalof the 8-field sequence type is described in Japanese Patent Disclosure(Kokai) No. 59-211315. In the conventional ghost cancelling system, inorder to extract the GCR signals (S₁)-(S₈) corresponding to eightfields, it is necessary to detect the first GCR signal (S₁) itself.However, with such a system, the construction of an S₁ line detectorwhich detects the arrival of the first GCR signal (S₁) is complicated.This is because, in order to detect the first GCR signal (S₁) itself,the following three conditions must all be fulfilled.

    ______________________________________                                        condition 1: the horizontal scanning line is                                               the 18H horizontal scanning line;                                condition 2: the GCR signal is a signal of                                                 waveform that rises steeply from                                              black to white, then falls                                                    smoothly from white to black                                                  (hereafter, WRB (Wide Reverse Bar)                                            waveform signal).                                                condition 3: the phase of the color burst                                                  signal is positive polarity (+).                                 ______________________________________                                    

Here, condition 1 can be detected using an ordinary line detectiontechnique. In contrast, detection of conditions 2 and 3 requirescomplicated processing to ascertain the shapes of the respectivewaveforms and determine their phase. Therefore, this requirement todetect conditions 2 and 3 made the construction of the conventional S₁line detection means complicated, making the system costly.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved ghost cancelling system in which waveform extraction can beperformed by line detection, without using complex-structured waveformdetection or phase detection.

It is a further object of the present invention to provide a ghostcancelling system which can eliminate the increased system costsresulting from complexity of the structure for waveform extraction.

In accordance with the present invention, the foregoing objects areachieved by providing a ghost cancelling system including a transversalfilter having a plurality of taps which coefficients are adjustablememory, wherein the tapped delay lines operate as an input portion ofthe transversal filter and delay the input signal by a specified delaytime. A line detector device detects a horizontal scanning line in whichthe reference signal is inserted from the signal of the input portion orthe output portion of the transversal filter. A reference signalextractor extracts the reference signal over 8 fields, starting with thehorizontal scanning line which is detected by the line detector device.A reference signal calculator finds a final reference signalcorresponding to the 8 field reference signals which are extracted bythe reference signal extractor, using a specified calculation algorithm.A ghost detection device detects the ghost signal using the finalreference signal calculated by the reference signal calculator device. Atap coefficient calculation device calculates the tap coefficient of thetransversal filter using the detection output of the ghost detectiondevice.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will becomemore apparent from the following detailed description of the presentlypreferred embodiment of the invention, taken in conjuction with theaccompanying drawings of which:

FIG. 1 is a basic block diagram of the ghost cancelling system accordingto the present invention;

FIG. 2 is a flow-chart showing the operating sequence of the ghostcancelling system shown in FIG. 1;

FIG. 3 is a detailed flow-chart showing the operating sequence of outputGCR waveform extraction and 8-field sequence calculation step shown inFIG. 2;

FIG. 4 is a view showing a memory map of FIG. 1;

FIG. 5 is a view given in explanation of the operation or FIG. 1;

FIG. 6 is a basic block diagram of the ghost cancelling system of asecond embodiment of the invention;

FIG. 7 is a detailed flow-chart showing the operating sequence of outputGCR waveform extraction and 8-field sequence calculation step of asecond embodiment of the invention;

FIG. 8 is a view given in explanation of the operation of FIG. 6; and

FIG. 9 is a detailed flow-chart showing the operating sequence of outputGCR waveform extraction and 8-field sequence calculation step of a thirdembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention will now be describedin more detail with reference to the accompanying drawings.

In an exemplary embodiment of the present invention, as illustrated inFIG. 1, there is provided a ghost cancelling system. The ghostcancelling system includes a transversal filter (hereafter, TF) 15, ananalogue/digital conversion circuit (hereafter, A/D conversion circuit)12, a microprocessor 17, ROM 18, RAM 19 and an output waveform memory20. ROM 18 is a memory element that stores the control program ofmicroprocessor 17. RAM 19 is a memory element that is used as workingmemory. The output waveform memory 20 is used for writing the ghostcancelling output waveform in real time. The TF 15 includes a pluralityof tapped delay lines 151, coefficient circuits 152 corresponding to thetapped delay lines 151, an adder 153 and a tap coefficient memory 154.

The video signal containing the GCR signal is supplied through an inputterminal 11 to the A/D conversion circuit 12, an 18H detection circuit31 and a clock generating circuit 14. The digital video signal that isoutput from the A/D conversion circuit 12, which is operated by clock CKof period T is input to the TF 15 in order for the ghost signal to becancelled from the video signal. The video signal that is input to theTF 15 is sequentially delayed with period T by the tapped delay lines151. Each of the outputs of this tapped delay lines 151 is multiplied bya tap coefficient C_(-m) -C_(n) by a respective correspondingcoefficient circuits 152. Then the results are added by the adder 153.This added output is supplied to an output terminal 16 and the outputwaveform memory 20 as the output of TF 15. A clock generating circuit 14generates a clock CK of the necessary period T for this system (e.g.,T=about 70 ns=1/4 f_(sc), f_(sc) =3.57954 MHz=chrominance sub-carrierfrequency).

The 18H detection circuit 31 detects the 18-th horizontal scanning line(18H). On receiving this detection result, an extraction control circuit21 instructs the microprocessor 17 and the output waveform memory 20 toperform waveform extraction to extract GCR signals for 8 fieldscontinuously, starting with 18H.

The operating sequence of this system is shown in FIG. 2. A basicdescription of the steps in FIG. 2 except for step B, in which the GCRsignal is extracted from the ghost cancelling signal and the 8-fieldsequence calculation is carried out, is given in "Ghost Clean System",IEEE Trans. on CE, Vol. CE-29, No. 3, Aug. 1983, by Murakami, Iga andTakehara (hereafter, Ref. 2).

First of all, on power-up or when the channel is changed (step Al),initial state setting processing such as resetting to zero the tapcoefficients C_(-m) -C_(n) that are latched in the tap coefficientmemory 154 of the TF 15 is performed (step A2). After this, theequalization loop indicated in steps B-A8 is executed. The details ofstep B are shown in FIG. 3. In step B1, the extraction of GCR signalsfor 8 fields continuously starts from 18H. The microprocessor 17 findsthe final GCR signal (S_(GCR)) by executing the processing from steps B2to B17 of FIG. 3. This processing for finging the final GCR signal(S_(GCR)) is described below.

First of all, the GCR signal (WRB waveform signal or black flat waveformsignal) Y₁ obtained by the first extraction is extracted into the outputwaveform memory 20, then stored in a waveform region {a} of the workingRAM 19 (step B2). The address of a waveform region {a} is shown in thememory map of FIG. 4. In step B3, the GCR signal Y₂ obtained by thesecond extraction is extracted into the output waveform memory 20, thensubtracted from the contents of waveform region {a}. The result of thissubtraction (Y₁ -Y₂) is stored in the waveform region {a}. In the nextstep, B4, the GCR signal Y₃ obtained by the third extraction isextracted into the output waveform memory 20, then stored in a waveformregion {b} of the working RAM 19. The address of the waveform region {b}is shown in the memory map of FIG. 4. In step B5, the GCR signal Y₄obtained by the fourth extraction is extracted into the output waveformmemory 20, then subtracted from the contents of the waveform region {b}.The result of this subtraction (Y₃ -Y₄) is stored in the waveform region{b}. In step B6, the GCR signal Y₅ obtained by the fifth extraction isextracted into the output waveform memory 20, then subtracted from thecontents of the waveform region {a}. The result of this subtraction (Y₁-Y₂ -Y₅) is stored in the waveform region {a}. In the following step,B7, the GCR signal Y₆ obtained by the sixth extraction is extracted intothe output waveform memory 20, then added to the contents of thewaveform region {a}. The result of this addition (Y₁ -Y₂ -Y₅ +Y₆) isstored in the waveform region {a}. In step B8, the GCR signal Y₇obtained by the seventh extraction is extracted into the output waveformmemory 20, then subtracted from the contents of the waveform region {b}.The result of this subtraction (Y₃ -Y₄ -Y₇) is stored in the waveformregion {b}. In next step B9, the GCR signal Y₈ obtained by the eighthextraction is extracted into the output waveform memory 20, then addedto the contents of the waveform region {b}. The result of this addition(Y₃ -Y₄ -Y₇ +Y₈) is stored in the waveform region {b}.

As a result, the contents indicated by equations (2) and (3) below,respectively, are stored in the waveform regions {a} and {b}.

    {a}=(Y.sub.1 -Y.sub.5)+(Y.sub.6 -Y.sub.2)                  (2)

    {b}=(Y.sub.3 -Y.sub.7)+(Y.sub.8 -Y.sub.4)                  (3)

Next, in step B10, addition result {α} and subtraction result {β} arefound by adding and subtracting the contents of the waveform regions {a}and {b}, as shown by equations (4) and (5) below. After this, as shownby equation (6) below, the difference Δ of the absolute values |ραi|,|μρi| of the respective sample values is found.

    {α}={a}+{b}                                          (4)

    {β}={a}-{b}                                           (5)

    Δ=|ραi|-|ρβi(6)

Here, the addition result {α} and the subtraction result {β} representthe positive polarity final GCR signal (S_(GCR)) or the negativepolarity final GCR signal (S_(GCR)) This will be explained using FIG. 5.

In FIG. 5, regarding the field number (i), numbers 1 to 8 are the sameas those shown in Ref. 1. Further numbers are directly increased insequence without repeated numbers. The GCR signal waveform is the sameas that of Ref. 1 except that GCR.sup.± of Ref. 1 is called W.sup.±.FIG. 5 shows the results of calculating

    Y.sub.i -Y.sub.i+4                                         (7)

    Y.sub.i+5 -Y.sub.i+1                                       (8)

    Y.sub.i+2 -Y.sub.i+6                                       (9)

    Y.sub.i+7 -Y.sub.i+3                                       (10)

for each field (i). In the calculated results, W and -W respectivelyindicate positive polarity and negative polarity WRB waveform signals.With this representation, it can be seen that the only combinations ofthe waveform regions {a} and {b} of odd fields (1,3,5,7, . . . ) are:(+2W, +2W), (+2W, -2W), (-2W, -2W) and (-2W, +2W). As shown by equations(4) and (5), one of the addition result {α} and subtraction result {β}of the waveforms {a} and {b} will therefore be ±4W (=±S_(GCR)), whilethe other is 0. Here, +4W indicates a positive polarity final GCR signal(S_(GCR)), and -4W indicates a negative polarity final GCR signal(S_(GCR)) Equation (6) is a calculation formula used to decide whetherthe addition result {α} is ±4W or the subtraction result {β} is ±4W. Instep B11, the microprocessor 17 uses this calculation result Δ to decidewhether the addition result {αβ is ±4W or the subtraction result {β} is±4W. That is, if Δ>0 (Δ=+4W), it decides that the addition result {α} is±4W, while if Δ>0 (Δ=-4W), it decides that the subtraction result {β} is±4W. Next, if Δ>0, in step B12, the microprocessor 17 decides whetherραi is positive or not. If it is positive, it takes {α} as S_(GCR) (stepB14). If it is not positive, it takes -{α} as S_(GCR) (step B13). In thesame way, if Δ>0, in step B13, it decides whether ρβi is positive ornot. If it is positive, it takes {β} as S_(GCR) (step B16). If it is notpositive, it takes -{β} as S_(GCR) (step B17). In general, the final GCRsignal (S_(GCR)) is constituted by 1k words (1 word=8 bytes), and isexpressed as a sample value by the following equation:

    S.sub.GCR ={S.sub.GCR }(k=0-1023)                          (11)

Next, in step A5, the microprocessor 17 calculate the difference signals{y_(k) } defined by equation (12) below and stores them in working RAM19.

    y.sub.k =S.sub.GCR+1 -S.sub.GCRk                           (12)

In step A6, the microprocessor 17 detects the position of the maximumpeak of the difference waveform signals {y_(k) } of the output. Theposition of this peak is denoted by p. That is, y_(p) is the peak of theimpulse of the main signal. In next step A7, after effecting alignmentat peak position (p), the microprocessor 17 finds an error waveformsignal {e_(k) } by subtracting from the difference waveform signal{y_(k) } of the output a reference waveform signal {r_(k) } that isstored beforehand in ROM 18, and stores this error waveform signal inworking RAM 19. This calculation is shown by the following equation(13).

    e.sub.k =y.sub.k -r.sub.k                                  (13)

In step A8, the tap coefficient is corrected based on the IncrementalControl method shown in equation (14) below.

    C.sub.inew =C.sub.iold +δ*sgn(e.sub.k)               (14)

Here, i=k-p, i=-m to n

Here, the suffix i of the tap coefficient (C_(i)) indicates the tap forcancelling the ghost of delay time iT seconds, and new and old indicate"before correction" and "after correction", respectively. And δ is apositive minute correction.

The ghost signal is cancelled from the video signal by repeatedexecution of the equalization loop consisting of the above sequence ofoperations (steps B-A8).

Accordingly, with this system, even if the leading GCR signal is not thefirst GCR signal (S₁) of the 8-field sequence, the final GCR signal(S_(GCR)) can still be found if simply the system is satisfied that itis the 18H GCR signal. For extraction of the GCR signal, it is thereforeonly necessary to detect 18H. This enables the extraction constructionto be simplified. Furthermore, the computation algorithm of FIG. 3 canbe performed by software of the microprocessor 17, so the hardware isnot made more complex in any way at all.

FIG. 6 is a block diagram showing the layout of a second embodiment ofthe present invention. FIG. 7 is a flow chart showing the calculationalgorithm for finding the final GCR signal (S_(GCR)). Items in FIG. 6and FIG. 7 which are the same as the corresponding items in FIG. 1 andFIG. 3 above are given the same reference numerals and a detaileddescription is omitted. The difference between FIG. 6 and FIG. 1described above is that a 281H detection circuit 41 is provided insteadof the 18H detection circuit 31 and that a different control program isstored in ROM 18. The characteristic parts of the control program areshown in FIG. 7.

In FIG. 6, the 281H detection circuit 41 detects 281H in each frame. Onreceiving this detection result, the extraction control circuit 21instructs the microprocessor 17 and the output waveform memory 20 toperform waveform extraction to extract GCR signals for 8 fieldscontinuously, starting with 281H. This processing is shown in step B21of FIG. 7. After this, the microprocessor 17 finds the final GCR signal(S_(GCR)) by executing the processing from steps B22 to B37 of FIG. 7.This processing for finding the final GCR signal (SGCR) is describedbelow.

First of all, in step B22, the GCR signal (WRB waveform signal or blackflat waveform signal) Y₁ obtained by the first extraction is extractedinto the output waveform memory 20, then stored in a waveform region {a}of the working RAM 19. In step B23, the GCR signal Y₂ obtained by thesecond extraction is extracted into the output waveform memory 20, thenstored in waveform region {b} in an inverted polarity condition. Next,in step B24, the GCR signal Y₃ obtained by the third extraction isextracted into the output waveform memory 20, then added to the contentsof waveform region {b} and stored in waveform region {b}. In step B25,the GCR signal Y₄ obtained by the fourth extraction is extracted intothe output waveform memory 20, then added to the contents of waveformregion {a} and stored in waveform region {a}. In step B26, the GCRsignal Y₅ obtained by the fifth extraction is extracted into the outputwaveform memory 20, then subtracted from the contents of waveform region{a} and stored in waveform region {a}. In next step B27, the GCR signalY₆ obtained by the sixth extraction is extracted into the outputwaveform memory 20, then added to the contents of waveform region {b}and stored in waveform region {b}. In step B28, the GCR signal Y₇obtained by the seventh extraction is extracted into the output waveformmemory 20, then subtracted from the contents of waveform region {b} andstored in waveform region {b}. In the following step B29, the GCR signalY₈ obtained by the eighth extraction is extracted into the outputwaveform memory 20, then subtracted from the contents of waveform region{a} amd stored in waveform region {b}. As a result, the contentsindicated by equations (21) and (22) below, respectively, are stored inwaveform regions {a} and {b}.

    {a}=(Y.sub.1 -Y.sub.5)+(Y.sub.4 -Y.sub.8)                  (21)

    {b}=(Y.sub.3 -Y.sub.7)+(Y.sub.6 -Y.sub.2)                  (22)

Next, addition result {α} and subtraction result {β} are found by addingand subtracting the contents of waveform regions {a} and {β}, as shownby equations (23) and (24) below. After this, as shown by equation (25)below, in step B30, the difference Δ of the absolute values |ραi|, |ρβi|of the respective sample values is found.

    {α}={a}+{b}                                          (23)

    {β}={a}-{b}                                           (24)

    Δ=|ραi|-|ρβi|(25)

Here, the addition result {α} and subtraction result {β} represent thepositive polarity final GCR signal (S_(GCR)) or the negative polarityfinal GCR signal (S_(GCR)). This will be explained using FIG. 8. FIG. 8shows the results, shown as FIG. 5, of calculating

    Y.sub.i -Y.sub.i+4                                         (26)

    Y.sub.i+3 -Y.sub.i+7                                       (27)

    Y.sub.i+2 -Y.sub.i+6                                       (28)

    Y.sub.i+5 -Y.sub.i+l                                       (29)

for each field (i). With this representation, it can be seen that theonly combinations of the waveform regions {a} and {b} of even fields(2,4,6, and 8, . . . ) are: (-2W, -2W), (-2W, +2W), (+2W, +2W), and(+2W, -2W). As shown by equations (23) and (24), one of the additionresult {α} and subtraction result {β} of the waveforms {a} and {b} willtherefore be ±4W (=±S_(GCR)), while the other is 0. In step B31, themicroprocessor 17 uses the calculation result Δ of equation (25) todecide whether the addition result {α} is ±4W or the subtraction result{β} is ±4W. Next, in step B32, if Δ>0, i.e., if the addition result {α}is ±4W, the microprocessor 17 decides whether ραi is positive or not. Instep B34, if it is positive, it takes {α} as S_(GCR). In step B35, if itis not positive, it takes -{α} as S_(GCR). In the same way, in step B33,if Δ is not >0, it decides whether ρβi is positive or not. In step B36,if it is positive, it takes {β} as S_(GCR). In step B37, if it is notpositive, it takes -{β} as S_(GCR).

Accordingly, with this system, the waveform extraction can be performedby detecting 281H.

FIG. 9 is a flow chart showing the operating sequence of a thirdembodiment of the present invention. In the foregoing embodiments, thecase was described in which the calculation algorithm to find the finalGCR signal (S_(GCR)) was executed irrespective of whether or not a GCRsignal was inserted in the video signal. In contrast, in the thirdembodiment, it is ascertained whether or not a GCR signal has beeninserted, and if it has not been inserted, the calculation algorithm isstopped. In order to achieve this object, in FIG. 9, a decision step C1and a result step C2 are inserted between step B10 and B11 of FIG. 3.

Specifically, in the case where a prescribed 8-field sequence GCR signalis inserted at 18H and 281H, one of the addition result {α} and thesubtraction result {β} is ±S_(GCR), and the other is 0. In step C1, itis therefore ascertained whether or not |Δ| larger than a specifiedvalue δ. If it is larger, it is concluded that a GCR signal is present,and control passes to step B11 so that processing is continued asbefore. If it is smaller than δ, in step C2, it is concluded that no GCRsignal is present, and the calculation algorithm is terminated.

As a result, with such a configuration, the calculation algorithm isterminated if there is no GCR signal, so a spurious operation resultingfrom no GCR signal being present is prevented. This modification can ofcourse also be applied to the second embodiment described above.

Numerous other modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstand that, within the scope of the appended claims, the presentinvention can be practiced in a manner other than as specificallydescribed herein.

For instance, in the above embodiments, the case is described in whichthe signal on the input side of the ghost cancelling system is input toline detection circuit 31 and 41. However, it would alternatively bepossible for the signal on the output side of the ghost cancellingsystem, that has been subjected to ghost cancel processing, to be inputthereto. Also, the present invention can of course be applied to asystem wherein the final GCR signal (S_(GCR)) is obtained with a reducednoise signal by repeated performance of the calculation between the 8fields.

What is claimed is:
 1. A ghost cancelling system wherein a ghost signalis cancelled from a video signal using a reference signal of the 8-fieldsequence type comprising:a transversal filter having a plurality of tapswith coefficients which are adjustable; a line detector for detecting ahorizontal scanning line in which said reference signal is inserted froma signal at an input portion of said transversal filter; a referencesignal extractor for extracting said reference signal over 8 fields,starting with said horizontal scanning line which is detected by saidlike line detector; a reference signal calculator for finding a finalreference signal corresponding to said 8 fields reference signals whichare extracted by said reference signal extractor, using a specifiedcalculation algorithm; a ghost detection means for detecting said ghostsignal using said final reference signal calculated by said referencesignal calculator; and a coefficient calculation means for calculatingsaid tap coefficients of said transversal filter using a detectionoutput of said ghost detection means.
 2. A system according to claim 1,further including a clock generating circuit for generating a clock CKof a period T.
 3. A system according to claim 1, wherein said linedetector detects a horizontal scanning line in which said referencesignal is inserted, in an odd-numbered field.
 4. A system according toclaim 1, wherein said reference signal calculator further including acalculating means and a signal output means, wherein the calculatingmeans performs the calculation indicated by the following equations

    a=(Y.sub.1 -Y.sub.5)+(Y.sub.6 -Y.sub.2)

    b=(Y.sub.3 -Y.sub.7)+(Y.sub.8 -Y.sub.4)

    α=a+b

    β=a-b

    Δ=α-β

Where Y₁ to Y₈ are respectively said first to eighth extractionreference signals, the signal output means outputs said final referencesignal in accordance with the polarities of the Δ and α, β.
 5. A systemaccording to claim 1, wherein said line detector detects a horizontalscanning line in which said reference signal is inserted, in aneven-numbered field.
 6. A system according to claim 5, wherein saidreference signal calculator further includes a calculating means and asignal output means, wherein the calculating means performs thecalculation indicated by the following equations:

    a=(Y.sub.1 -Y.sub.5)+(Y.sub.4 -Y.sub.8)

    b=(Y.sub.3 -Y.sub.7)+(Y.sub.6 -Y.sub.2)

    α=a+b

    β=a-b

    Δ=α-β

where Y₁ to Y₈ are respectively said first to eighth extractionreference signals, the signal output means outputs said final referencesignals in accordance with the polarities of the Δ and α, β.
 7. A systemaccording to claim 1, further including an analog/digital conversioncircuit for converting said video signal into a digital signal andsupplying the converted signal to said transversal filter.
 8. A systemaccording to claim 1, wherein said coefficient calculation meanscorrects said tap coefficients incrementally.
 9. A method forcontrolling a ghost cancelling system having a transversal filtercomprising:cancelling a ghost signal utilizing tap coefficients obtainedfrom a video signal containing a reference signal of the 8-fieldsequence type, including the steps of: detecting a horizontal scanningline containing said reference signal of the 8-field sequence type;extracting said reference signal of the 8-field sequence type from saiddetected horizontal scanning line; calculating a final reference signalcorresponding to said reference signal of the 8-field sequence type;distinguishing said ghost signal using said final reference signal; andcorrecting said tap coefficients in response to said distinguished ghostsignal.